5.7 Vortec Runs Great On Land but Bogs Under Load in Water

[Scott Danforth]

That’s true then on older boats you have Quadrajets which are totally different from those 2.

you are old...... LOL..... then again, I remember the Holley 3-barrel.

 

[Scott06]

No power piston. Just mains and secondary jets and vac powered needles on the main jets.

the piston that the step up rod is attached to , its what the vacuum pulls down and release to be lean or rich.

 

[Scott06]

The reason I suggested the engine builders Holley video is to UNDERSTAND how a carburetor functions. How the power valve interacts with other components, how jet sizes are determined. Once you understand how or the physics troubleshooting becomes efficient vs monkey see monkey try.

This is the Bible for edlbrock carbs https://www.edelbrock.com/pub/media/wysiwyg/documents/carb-owners-manual.pdf

 

[tank1949]

@Scott06 it'll go into gear and i can roll around up to roughly 1500-1700 RPM but anything higher and it wants to bog down and die so I'll come off it and it'll keep running.

I pulled the plugs today and all but one we're decently black like it's running rich. One plug was pretty clean however so wondering if that one maybe wasn't firing. The wires were in all the right places. I'll post some pics later. I'm pretty certain the fuel pump is keeping constant pressure to the engine.

Based on all of your comments I'm going to start with the following

1. Change all spark plugs
2. Change all plug wires
3. change the distributor cap and maybe the ignition sensor
4. Once it's back together i'll get a vacuum gauge on it and see what's happening with the fuel/air mix.

I need to inspect the anti-siphon fitting but not sure where that might be. I have two tanks that feed into a switched diverter so i can be between tanks then from there it feeds to the fuel pump then to the fuel filter and then into the carb. I replaced the fuel filter and the pre-filter to make sure it wasn't clogged.

check fuel vent for mud-dobber mud.

 

[Rick Stephens]

This is the Bible for edlbrock carbs https://www.edelbrock.com/pub/media/wysiwyg/documents/carb-owners-manual.pdf

Never heard it called a power piston. Not that you're wrong, just never heard it called that before.

I have and know, relatively front to back, the Edelbrock manual. At least to the extent my old old brain cells do recalls. Good stuff.

 

[carrera205]

 

[Scott Danforth]

Any electrode that is white is either not getting fuel, or has water in the cylinders

 

[Scott06]

Any electrode that is white is either not getting fuel, or has water in the cylinders

I noticed on my vortec that the electrode discoloration is not consistent around the entire electrode, which is kind of what i see here . I get more of a brownish, and im running a tad on rich side (13.25-13.5 afr at cruise , 12.0-12.5 at wot)

 

[Scott06]

Never heard it called a power piston. Not that you're wrong, just never heard it called that before.

I have and know, relatively front to back, the Edelbrock manual. At least to the extent my old old brain cells do recalls. Good stuff.

Yeah not 100 % sure edlebrock calls it a step up piston. Power piston may be a hold over from my rochester 2 jet/ mercarb days … either way we are talking about the same thing.